1. Field of the Invention
The invention concerns a plane, for example, printed-circuit or microstrip, antenna radiating circularly or linearly polarized waves. The invention may be applied to the excitation of a circular or linear polarization waveguide.
An antenna of this kind in accordance with the invention provides a compact transition between TEM (transverse electromagnetic) feedlines such as triplate (i.e., a suspended stripline), microstrip, coaxial, bar-line feedlines (this list is not exhaustive) and free space (or a waveguide).
2. Description of the Prior Art
Known systems for providing a transition between a TEM guided wave and free space comprise:
systems made up of an exciter and a horn: the overall size is then large (length greater than a wavelength), PA1 microstrip antennas: the overall size is then reduced (length less than a half-wavelength). PA1 Double resonators of square, circular, etc. shape fed by orthogonal coaxial feedlines. The excitation feedlines render the radiation asymmetrical. Also, a device of this kind involves soldering. PA1 Double or single resonators respectively fed by a linear slot or a coupling hole. A device of this kind does not require any soldering. Also, the excitation does not render the diagram asymmetrical if the coupling slot or hole is disposed symmetrically to the resonator (of square, circular, etc. shape). In the case of a circularly polarized wave or double linear polarization it is then necessary to render the excitation asymmetrical or to cross the feedlines (cross-shape slot). PA1 Electromagnetic coupling. A device of this kind does not require any soldering. Radiation is degraded by radiation from the line on the radiating side. PA1 Resonators disposed at the bottom of the guide. The performance, bandwidth and polarization purity are then rarely compatible with telecommunication bands. PA1 Double resonators fed by coaxial feedlines. A device of this kind requires three different stages: PA1 increased bandwidth, PA1 very pure polarization for circular or linear polarization with one or two ports, PA1 very symmetrical excitation, the feedlines being screened on the excited wave side.
The antenna in accordance with the invention is a microstrip antenna offering improved performance.
Known devices in this category comprise:
Known compact systems providing a transition between a TEM guided wave and a wave guide comprise:
TEM line excitation stage, PA2 active resonator stage, PA2 passive resonator stage.
In French patent application No 87 15359 the device for exciting a guide has two stages only for performance equivalent to that of a conventional diplexer and does not require any soldering.
An object of the invention is to improve the specifications of the prior art device.